System and method for measuring essential power amplification functions

ABSTRACT

An apparatus includes a device under test, a network analyzer, an internal amplifier, a first switch, a second switch, a third switch, a first air-line directional coupler, and a first attenuator. A method of characterization measurement includes providing a harmonics signal from the device under test to a spectrum analyzer, providing a generated signal and a reflected signal to a first receiver disposed within a network analyzer, and recording a parameter deviation of the network analyzer.

BACKGROUND

Various measurements need to be taken on a completed power amplifier(PA) to fully characterize the PA and determine that the PA is suitablefor service. Those measurements include: input and output power; hots-parameters (S11, S21, S22); adjacent channel power ratio (ACLR);spectrum emission masks (SEM); error vector magnitude (EVM); andharmonics and spurious measurements (up to about the 5^(th) or 6^(th)harmonic). In addition, the following measurements need to be taken onlow power devices under test (DUTs) that makeup part of a PA (poweramplifiers, filters, attenuators, and the like): normal (small-signal)s-parameters (s11, s21, s22) and input and output power.

Previous methods of performing the above tests have required eitherseparate setups, where the DUT is connected to first one measuringinstrument and then the other, or setups where the DUT is switchedbetween setups, requiring a high-power RF switch at its output. Thisswitch can be a source of unreliability due to the degradation ofinternal switch contacts when high RF power is run through them andespecially in the case where the RF power is switched withoutmomentarily turning it off (“hot switching”).

One previous method found in the Anritsu “PATS” test set has twoinherent disadvantages. One disadvantage is that high cost directionalcouplers at the output of the DUT must pass harmonics up to 13 GHz onits coupled port while handling high power on its through line. Anotherdisadvantage is that the small-signal s22 and “hot” S22 measurements areless accurate because the power level from network analyzer source thatprobes the DUT output is approximately plus 5 dBm (or about 45 dB belowthe DUT output signal). When reduced by a DUT return loss of perhaps 20dB the return signal is now 65 dB below the DUT carrier output and isdifficult to select and measure accurately. The problem is aggravatedwhen testing a DUT with a very good return loss of more than 20 dB.

Another prior method found in a JRC proposal for a high-power amplifiertester uses a “N by 2” switch matrix to multiplex N DUTs into twomeasuring ports. One port is connected to a vector network analyzer(VNA) for “hot” s22 injection measurements. The other port is connectedto a spectrum analyzer and power meter for spectrum harmonics and powermeasurements. The switches that are required to switch the DUT outputsignal between these ports need to be high-power switches and aresubject to “hot-switching” situations leading to early failure.

What is needed is a combination of essential power amplifier measurementfunctions and measurement systems self-test capability into one RFcircuit without the need for high-power RF switches or DUTdisconnections providing for high reliability, high repeatability, lowcosts, and high accuracy.

SUMMARY

One advantage of embodiments described in present application is thatonly one test setup is required to perform a variety of characterizationmeasurements. Another advantage of embodiments described herein is thatcalibration can be performed without any physical changes to the testsetup. Other advantages are apparent from the description herein.

These and other advantages are achieved, for example, in an apparatusthat includes an internal amplifier coupled to a network analyzer, afirst switch coupled between the internal amplifier and the networkanalyzer, a second switch coupled between the internal amplifier and thenetwork analyzer, a third switch coupled between a device under test andthe network analyzer, a first air-line directional coupler coupledbetween the second switch and the device under test, and a firstattenuator coupled to the first air-line directional coupler.

These and other advantages are also achieved, for example, in a systemthat includes the apparatus described above, a network analyzer coupledto the apparatus, and a device under test coupled to the apparatus.

These and other advantages are further achieved, for example, in asystem that includes a network analyzer, a device under test having aninput and an output, an internal amplifier, having an input and anoutput, coupled to the network analyzer, a first switch coupled betweenthe input of the internal amplifier and the network analyzer, a secondswitch coupled between the output of the internal amplifier and thenetwork analyzer, a third switch coupled between the input of the deviceunder test and the network analyzer, a first air-line directionalcoupler, having an input, a main-line output, and a coupled-line input,coupled between the second switch and the output of the device undertest, and a first attenuator coupled to the main-line output of thefirst air-line directional coupler, wherein the attenuator is ahigh-power attenuator.

These and other advantages are achieved, for example, in a method thatincludes providing a first signal at a predetermined first frequency toan input of a device under test. The first signal is provided by ameasurement interface device. The method further includes receiving aharmonics signal at the measurement interface device from an output ofthe device under test and passing the harmonics signal through an inputport of a main-line of a first air-line directional coupler disposedwithin the measurement interface device. The method also includesproviding the harmonics signal from an output port of the main-line ofthe first air-line directional coupler to a spectrum analyzer coupled tothe measurement interface device.

These and other advantages are also achieved, for example, in a methodthat includes providing a first signal at a predetermined firstfrequency to an input of a device under test. The first signal drivesthe device under test to full power output. The method also includesproviding a second signal at a predetermined second frequency to aninput of an internal amplifier disposed within a measurement interfacedevice to provide an amplified second signal and providing the amplifiedsecond signal to a wideband isolator disposed within the measurementinterface device to provide an isolated second signal. The methodfurther includes passing the isolated second signal through acoupled-line of a first air-line directional coupler to a main-line ofthe first air-line directional coupler disposed within the measurementinterface device to provide a coupled second signal and providing thecoupled second signal to an output of the device under test. The deviceunder test reflects a portion of the coupled signal as a first reflectedsignal. The method also includes passing the first reflected signalthrough an input port of a main-line of a second air-line directionalcoupler disposed within the measurement interface device to acoupled-line of the second air-line directional coupler to provide afirst coupled reflected signal and providing the first coupled reflectedsignal from an output port of the coupled-line of the second air-linedirectional coupler to an attenuator to produce a first attenuatedreflected signal. The method further includes providing the firstattenuated reflected signal to a first receiver disposed within anetwork analyzer coupled to the measurement interface device.

These and other advantages are further achieved, for example, in amethod that includes steps of directly coupling an input port to anassociated output port in a network analyzer, connecting a first cableto a first interface port in the network analyzer and connecting asecond cable to a second interface port in the network analyzer. Thefirst cable terminates at a first unconnected end with a firstcalibration standard. The second cable terminates a second unconnectedend with a second calibration standard. The method also includesinitiating a calibration program and recording a parameter deviation ofthe network analyzer, the first cable, and the second cable.

DESCRIPTION OF THE DRAWINGS

The detailed description will refer to the following drawings, whereinlike numerals refer to like elements, and wherein:

FIG. 1 is a block diagram of a power amplifier measurement system;

FIG. 2 is a schematic of a precision system interface for use in thepower amplifier measurement system;

FIG. 3 is a diagram of a vector network analyzer for use in the poweramplifier measurement system;

FIG. 4 is a schematic illustrating connections between the precisionsystem interface and the vector network analyzer;

FIG. 5 is a flowchart illustrating a method for independent operation ofthe vector network analyzer;

FIG. 6 is a schematic indicating jumpers used for independent operationof the vector network analyzer when the analyzer is not used in thepower amplifier measurement system;

FIG. 7 is a schematic illustrating switch positions in the precisionsystem interface for independent operation of the vector networkanalyzer;

FIG. 8 is a block diagram illustrating system setup for signal generatorto device under test path characterization;

FIG. 9 is a block diagram illustrating de-embedding of a device undertest adapters for path characterization;

FIG. 10 is a diagram of the s-parameter measurement of the testadapters;

FIG. 11 is a flowchart describing a method for path characterization;and

FIGS. 12A and 12B are flowcharts describing a method for measurementinstrument calibration;

FIG. 13 is a schematic illustrating signal propagation through theprecision system interface for input and output power measurements;

FIG. 14 is a schematic illustrating signal propagation through theprecision system interface for vector spectrum analysis measurements;

FIG. 15A is a schematic illustrating signal propagation through thevector network analyzer for hot S11 measurements;

FIG. 15B is a schematic illustrating signal propagation through theprecision system interface for hot S11 measurements;

FIG. 16A is a schematic illustrating signal propagation through thevector network analyzer for hot S21 measurements;

FIG. 16B is a schematic illustrating signal propagation through theprecision system interface for hot S21 measurements;

FIG. 17A is a schematic illustrating signal propagation through theprecision system interface for hot S22 measurements;

FIG. 17B is a schematic illustrating signal propagation through thevector network analyzer for hot S22 measurements;

FIG. 18A is a schematic illustrating signal propagation through thevector network analyzer for small-signal s11 measurements;

FIG. 18B is a schematic illustrating signal propagation through theprecision system interface for small-signal s11 measurements;

FIG. 19A is a schematic illustrating signal propagation through thevector network analyzer for small-signal s21 measurements;

FIG. 19B is a schematic illustrating signal propagation through theprecision system interface for small-signal s21 measurements;

FIG. 20A is a schematic illustrating signal propagation through thevector network analyzer for small-signal s22 measurements; and

FIG. 20B is a schematic illustrating signal propagation through theprecision system interface for small-signal s22 measurements.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an embodiment of a power amplifiermeasurement system (“measurement system”) for taking essentialcharacterization measurements of a power amplifier or, in general,devices under test such as preamplifiers, filters and attenuators. Themeasurement system, designated generally by reference number 10,includes: Precision System Interface 20; Vector Network Analyzer 30;device under test 40; Test Port 1 44; Test Port 2 48; external lineardriver amplifier 50; signal generator 60; spectrum analyzer 70; firstpower meter 80; and second power meter 90.

FIG. 2 is a schematic of an embodiment of Precision System Interface(PSI) 20. PSI 20 includes internal booster amplifier 100; directionalcouplers 110, 120, and 150; air-line directional couplers 130 and 140;attenuators 160 and 180; high-power attenuator 170; wide band isolator190; and switches 200, 210, 220, 230, 240, and 250. PSI 20 also includesports designated J1 through J18. Although illustrated separately in FIG.1, Test Port 1 44 and Test Port 2 48 are actually preferably part of PSI20, allowing the device under test (DUT) 40 to connect directly to PSI20. By connecting DUT 40 to PSI 20, any characterization measurements ofDUT 40 can be made without switching the testing setup since PSI 20 actsas a measurement interface between DUT 40 and any signal generation ormeasurement equipment.

The air-line directional couplers 130 and 140 have a main-line inputport, a main-line output port and coupled-line port. The main-line inputport is denoted by the label “IN”. An internal main-line conductor(“main-line”) from the main-line input port to the main-line output portis built from suspended stripline, so that the surrounding dielectricmaterial is air. This enables the air-line directional coupler to carryhigh power with low loss and also to have a broad frequency response. Asignal entering at the main-line input port will not degradesignificantly before it exits the main-line output port. This is opposedto a printed stripline-on-board type of construction whose frequencyresponse would degrade more as the frequency increases.

The coupling function in most directional couplers is accomplished by alength of conductor (“the coupled-line”) parallel to the main-line, andapproximately one quarter wavelength long. The coupled-line is coupledto the main-line and is connected to the coupled-line port. For example,at 1.5 GHz, the center frequency of the specified band, the conductor isabout five centimeters long. Frequencies in this band will couple to thecoupled-line only in one direction at 10, 20 or 30 dB lower power,depending on the model. A small portion of the main energy is coupledoff onto the coupled-line while the main signal itself is relativelyunaffected. For instance, a 20 dB coupler will transmit about 99 percentof the incoming energy to its main-line output port, and 1% to thecoupled port. If power is input into the main-line output port, however,almost no power (i.e., only 0.01 percent) will be coupled to thecoupled-line port, hence the name “directional” coupler.

Although the coupling function of the air-line directional couplers 130and 140 is only rated “in-band” (from 0.8 to 2.2 GHz, for example) andfalls off rapidly on either side of that band (due to the quarterwavelength relationship), the main-line performs well through at least13 GHz. High-power couplers that perform as well on their coupled-lineas on their main-line (to allow harmonics measurements at thecoupled-line) are much more expensive than air-line narrow-banddirectional couplers. Using air-line narrow-band directional couplersallows measurement of harmonics (e.g., 2×2 GHz=4 GHz, 3×2 GHz=6 GHz, upto the 6^(th) harmonic of 2 GHz=12 GHz) using a spectrum analyzerwithout much degradation for much lower costs. In a preferredembodiment, only air-line directional couplers 130 and 140 need to passfrequencies on their main-lines that are higher than their ratedfrequency band of their coupled-lines. The coupled-line of alldirectional couplers is reciprocal. When a signal is input into thecoupled-line port, a reduced version of the signal will appear at themain-line input but not at the main-line output.

FIG. 3 shows an embodiment of Vector Network Analyzer (VNA) 30. VNA 30includes: source generator 300; switch splitter leveler 310; stepattenuators 320, 322, 324, and 326; A Receiver 330; R1 Receiver 332; R2Receiver 334; and B Receiver 336. VNA 30 also includes: VNA Port 1 340and VNA Port 2 344. VNA 30 further includes ports A Source Out 350; ACoupler In 352; A Out 354; A In 356; R1 Out 358; R1 In 360; R2 Out 362;R2 In 364; B In 368; B Out 370; B Coupler In 372; and B Source Out 374.The dotted line in FIG. 3 denotes the front panel of VNA 30. All of theconnections shown to the right of the dotted line are external ports onthe front panel of VNA 30 that allow user access to the internalreceivers and couplers.

The switch splitter leveler 310 has two functions. The switch splitterleveler 310 takes a signal generated by source generator 300 and directsthe signal to either VNA Port 1 340 or VNA Port 2 344. The switchsplitter level 310 can also divide the signal generated by sourcegenerator 300 into a signal that exits VNA 30 through VNA Port 1 340 orVNA Port 2 344 and a signal that goes to reference receiver R1 Receiver332 or reference receiver R2 Receiver 334, so that ratio measurementsmay be made. For example, small-signal s11=“A” Receiver signal dividedby R1 signal. In this way, the signal being measured by the referencereceivers R1 Receiver 332 and R2 Receiver 334 can be derived eitherdirectly from the source generator 300 or from signals propagatingthrough PSI 20 during characterization measurement operations of thedevice under test 40, as described below.

FIG. 4 is a schematic illustrating how PSI 20 connects with VNA 30 in anembodiment of measurement system 10. PSI 20 connects to VNA Port 1 340and VNA Port 2 344 using PSI 20 ports J14 and J6, respectively. PSI 20also connects with port A Source Out 350 of VNA 30 using port J7 and toport A Coupler In 352 of VNA 30 using port J12. PSI 20 further connectsto port R1 In 360 using port J9 of VNA 30 and to port R1 Out 358 of VNA30 using port J8. PSI 20 connects to port R2 In 364 of VNA 30 using portJ10 and to port R2 Out 362 of VNA 30 using port J11. PSI 20 alsoconnects to port B In 368 of VNA 30 using port J18 and to port B Out 370of VNA 30 using port J17.

FIG. 5 is a flowchart illustrating an embodiment of a method forcalibrated independent operation of the VNA 30, designated generally byreference number 400. Independent operation method 400 includes thesteps of: connecting all associated VNA “IN” and “OUT” ports, step 410;connecting “path characterization” (PC) cables to VNA Ports 1 and VNAPort 2, step 420; initializing the VNA internal calibration program,step 430; connecting the first “calibration standard” to open end of PCcables, step 440; running internal calibration, step 450; recordings-parameter deviation in calibration file, step 460; determining whetherthe last calibration standard has been connected, step 470; connectingthe next calibration standard to open-ends of the PC cables, step 480;and ending the VNA internal calibration program, step 490.

The independent operation of VNA 30 is necessary for high accuracymeasurements of low-power devices under test, or, more importantly, formeasuring path loss in PSI 20 for calibration purposes before the systemis ready to accurately measure DUT 40. In order to facilitateindependent operation of VNA 30 all associated in and out ports of VNA30, are connected to each other, step 410. For example, port A SourceOut 350 and port A Coupler In 352 are connected to each other, port AOut 354 and port A In 356 are connected to each other, and port R1 Out358 and port R1 In 360 are connected to each other.

Connection of the associated VNA 30 ports may be accomplished in twoways: using jumper cables or using PSI 20. FIG. 6 show how these portconnections may be accomplished using jumper cables. For example, ASource Out 350 and A Coupler In 352 may be connected using jumper 380A.R1 Out 358 and R1 In 360 may be connected using jumper 380C. R2 Out 362and R2 In 364 may be connected by jumper 380D. Also B In 368 and B Out370 may be connected by jumper 380E.

In addition to the jumper cables to make the VNA port connections, FIG.7 shows how these port connections may be accomplished directly usingPSI 20. For example, A Source Out 350 and A Coupler In 352 may beconnected using ports J7 and J12 of PSI 20 along path I by settingswitches 200 and 210 to their 2-1 and 1-2 positions, respectively. R1Out 358 and R1 In 360 may be connected using ports J8 and J9 of PSI 20along path II by setting switch 220 to position 1-2. R2 In 364 and R2OUT 362 may be connected using ports J10 and J11 of PSI 20 along pathIII by setting switch 250 to position to 1-C. Furthermore, B Out 370 andB In 368 may be connected using ports J17 and J18 of PSI 20 along pathIV by setting switch 240 to position 2-C.

Referring back to FIG. 5, after the VNA IN and OUT ports have beenconnected, PC cables are connected to VNA Port 1 340 and Port 2 344,step 420. A “calibration reference plane” is then defined at the openends of the PC cables. VNA internal calibration program is initialized,step 430, in order to perform calibration of the VNA 30. A first set ofcalibration standards is connected to the open ends of the PC cables,step 440. These calibration standards may include opens, shorts, and 50ohm loads. Calibration may also be performed by connecting the ends ofthe PC cables together for a through reading. After connecting the firstset of calibration standards to the open ends of the PC cables, step440, the internal calibration program is run, step 450. This causes thes-parameter deviation of the VNA for the first set of calibrationstandards to be recorded in a calibration file, step 460. Thecalibration program then determines whether the last calibrationstandard has been connected to the PC cables, step 470. If the lastcalibration standard has not been connected, the next set of calibrationstandards is connected to the open end of the PC cables, step 480. Ifthe last set of calibration standards has been connected, the VNAinternal calibration program is ended, step 490.

The VNA internal calibration program is programmed to know the “ideal”calibration standards that should be measured for VNA 30 and records thedifference from the actual s-parameters it “sees” at the end of the PCcables. The VNA internal calibration program stores these differences ina calibration file so that when actual measurements are made with theVNA and the PC cables, the effect of the VNA and the PC cables will besubtracted out by the differences stored in the calibration file. TheVNA 30 will thus display the s-parameters that actually exist at thedevice under test to which the PC cables are connected. Once VNA 30 plusthe PC cables are calibrated, independent calibrations may be run on anyof the measurement devices being used to characterize the DUT 40.

In addition to calibration of VNA 30, path characterization must beperformed on the rest of measurement system 10. A path is defined as theroute between a measurement instrument, i.e., signal generator 60, tothe measurement instrument test ports or from the measurement instrumenttest ports to DUT 40 test ports 44 and 48. Performing pathcharacterization preserves the instrument accuracy at system 10 testports. There are five paths for non-VNA measurements: signal generatorto DUT input; signal generator to power meter; DUT input to power meter;DUT output to spectrum analyzer; and Amplifier Distortion Test Set(ADTS) reference to DUT paths (for delay measurements only). These fivepaths are characterized in terms of phase and amplitude. Each path istreated as a device and measurements are done using the VNA.

These paths can potentially be non-insertible. If a device (e.g., DUT40) uses a different type of connector than the connectors used on thetest port (e.g. test ports 44, 48) cables, the device cannot connect tothe test cables without using adapters. Such a device is called anon-insertible device. Even in a situation in which the deviceconnectors and the test cable connectors are of the same type, thedevice could become non-insertible if the device's connector does nothave the opposite connector “sex” than the connector on the test cableport. For example, if the device has an SMA female connector on thedevice's input port and the connector on the test port cable also has aSMA female connector, then the device is non-insertible.

FIG. 8 is a block diagram illustrating the measurement system 10 forsignal generator 60 to DUT 40 path characterization measurements. PSI 20is used to connect signal generator 60 and DUT 40, as describedpreviously. The path is characterized in terms of s-parameters.Subsequent correction for the path permits correction for path loss andalso mismatch loss at the signal generator 60 and the DUT 40 input.

As mentioned previously, the paths are potentially non-insertible. Testadapters can be used to make the connection between the measurementequipment and the DUT 40. However, when performing characterizationmeasurements on the device, the adapters may not be used (depending onthe device connector configuration). Therefore, the effect of theadapters used during calibration has to be removed during thecharacterization measurement procedure. In situations in which adaptersare used on the VNA PC cables, the effect of the adapters are removed byembedding techniques. Embedding allows the calibration reference planeto be moved from the end of the adapter to the end of the test portcable connector.

FIG. 9 illustrates two test adapters, Adapter A 510 and Adapter B 520,which are used to connect VNA 30 to DUT 40 during system calibration.Embedding moves the effective calibration reference plane to the end ofAdapter A 510 and Adapter B 520 mathematically by using an adaptermodel. The adapter information is “embedded” in the VNA calibrationfiles, where the information can be subtracted from the DUT 40characterization measurements to obtain the actual DUT 40characterization parameters. The reverse of this embedding process iscalled “de-embedding”.

Initially, VNA 30 is calibrated as described previously, with referenceto FIG. 6. The error terms from VNA 30 are read and modified using thetest adapters s-parameters. The modified error terms are written back toVNA 30, which allows the calibration reference plane to move from theend of the PC cables to the end of the adapters. The s-parametermeasurement of the test adapters is illustrated in FIG. 10.

FIG. 11 is a flow chart describing an embodiment of a method for pathcharacterization. The path characterization method, denoted generally byreference number 600, includes: performing VNA 30 calibration, step 400(see FIG. 5); de-embedding the test adapters, step 610; performingmeasurement instrument calibrations, step 620; connecting VNA 30 to PSI20, step 630; connecting the test adapters to DUT 40, step 640;embedding the test adapters, step 650; and removing the test adaptersfrom DUT 40, step 660.

VNA 30 calibration, step 400, is performed as described previously, withreference to FIG. 5. The test adapters are de-embedded, step 610,according to the method described above, with reference to FIG. 9. Thevarious paths are then characterized and calibrated, step 620, asdescribed in detail with reference to FIGS. 12A and 12B. VNA 30 isconnected to PSI 20, step 630, and the test adapters are connected tothe PC cables of DUT 40, step 640. The test adapters are then embeddedas described above, with reference to FIG. 9. The test adapters are thenremoved from DUT 40, step 660, so that DUT 40 can be reconnected to PSI20 for characterization measurement operation of measurement system 10,as described below.

FIGS. 12A and 12B illustrate flow charts describing an embodiment of amethod for measurement instrument calibration corresponding to step 620in FIG. 11. After the test adapters have been de-embedded (step 610 inFIG. 11), VNA Port 1 340 cable is connected to signal generator 60 cable(at signal generator 60 end, as shown in FIG. 8), step 700, and VNA Port2 cable is connected to the input cable of DUT 40, step 710, as shown inFIG. 8. The path characterization and path loss, or calibrationmeasurements, between the end of the signal generator 60 cable and theend of the DUT 40 input cable, is then performed, step 720. The pathcharacterization and path loss, or calibration measurements areperformed by taking the s-parameter measurements of the path. VNA Port 2cable is then connected to first power meter 80 connector on PSI 20,port J13, and calibration measurements performed, step 730. The pathcharacterization and path loss, or calibration measurements, between thesignal generator 60 and first power meter 80, is then calculated, step740, by taking the difference between the calibration measurementsperformed at steps 720 and 730.

VNA Port 1 340 is then connected to the end of DUT 40 output cable, step750, and VNA Port 2 is connected to second power meter 90 connector onPSI 20, port J5, step 760. The path characterization and path loss, orcalibration measurements, between DUT 40 and the second power meter 90,is then performed, step 770, as shown in FIG. 12B. VNA Port 2 is thenconnected to the spectrum analyzer 70 cable (at the spectrum analyzer 70end of the cable), step 780. The path characterization and path loss, orcalibration, between DUT 40 and the spectrum analyzer 70 is thenperformed, step 790.

FIG. 13 is schematic illustrating signal propagation through PSI 20 forinput and output power measurements. Signal generator 60 generates aninput power signal, which enters PSI 20 at port J1 and exits PSI 20 atport J2, denoted by path AI. The signal is amplified by external lineardriver amplifier 50. The amplified signal reenters PSI 20 at port J3 andtravels to directional coupler 120 along path AII. The amplified signalenters the main-line input of directional coupler 120 and a coupledsignal exits the coupled-line output of directional coupler 120. Thesignal then exits PSI 20 at port J13 along path AIII and is measured byfirst power meter 80. The amplified signal exits the main-line output ofdirectional coupler 120 and passes through switch 230 in the 1-Cposition along path AIV. The signal exits PSI 20 at port J5 and passesthrough Test Port 1 44 to enter the input of the DUT 40 along path AV.The signal exits the output of the DUT 40 and passes through Test Port 248 along path AVI entering PSI 20 at port J16. The output signal entersair-line directional coupler 140 along path AVII and is coupled off byair-line directional coupler 140, exiting 140 at the coupled-lineoutput. The coupled output signal travels along path AVIII to enter theinput of directional coupler 150. The output signal is further coupledby directional coupler 150 and exits the coupled-line output ofdirectional coupler 150. The coupled signal exits PSI 20 at port J5along path AIX and is measured by second power meter 90.

FIG. 14 is a schematic illustrating signal propagation through PSI 20for Vector Spectrum Analysis Measurements. Signal generator 60 generatesan input signal at frequency F1, which enters PSI 20 at port J1 andexits PSI 20 at port J2, denoted by path BI. In one embodiment, theinput signal is amplified by external linear driver amplifier 50. Theamplified signal re-enters PSI 20 at port J3 and travels to directionalcoupler 120 along path BII. The amplified signal passes throughmain-line of directional coupler 120. The signal passes through switch230 in the 1-C position and exits PSI 20 at port J15 along path BIII.The signal passes through Test Port 1 44 and enters the input of DUT 40along path BIV. A generated harmonics signal exits the output of DUT 40and passes through Test Port 2 48 along path BV. The harmonic signalenters PSI 20 at port J16 and passes through the main-line input ofair-line directional coupler 140 along path BVI. The harmonic signalexits the main-line output of air-line directional coupler 140 andpasses through the main-line input of air-line directional coupler 130along path BVII. The signal exits the main-line output of air-linedirectional coupler 130 and passes through high-power attenuator 170along path BVIII. The attenuated harmonic signal exits high-powerattenuator 170 along path BIX and exits PSI 20 at port J4. Theattenuated harmonic signal is then measured by spectrum analyzer 70.FIGS. 15A and 15B are schematics illustrating signal propagation throughVNA 30 and PSI 20 for hot S11 measurements. As shown in FIG. 15A, VNAsource 300 generates a drive signal which enters switch splitter leveler310 along path CI. The signal exits switch splitter leveler 310 alongpath CII and, in one embodiment, is attenuated by step attenuator 320.The attenuated signal travels along path CIII and exits VNA 30 at ASource Out 350.

The attenuated signal enters PSI 20 at port J7, as shown in FIG. 15B,and travels along path CIV passing through switch 200, with switch 200in the 2-3 position. The signal enters the input of internal amplifier100 and the amplified signal exits 100 along path CV. The amplifiedsignal passes through the main-line input of directional coupler 110along path CVI passing through switch 210, with switch 210 in the 3-2position. The amplified signal continues to travel along path CVI andexits PSI 20 at port J12.

As shown in FIG. 15A, the amplified signal enters VNA 30 at A Coupler In352 and travels along path CVII, exiting VNA 30 at Port 1 340. Theamplified signal re-enters PSI 20, as shown in FIG. 15B, at port J14 andtravels along path CVIII through switch 230, with switch 230 in the 2-Cposition. The amplified signal exits PSI 20 at port J15 and, passingthrough Test Port 1 44 along path CIX, enters the input of DUT 40. Theamplified signal entering the input of DUT 40 drives DUT 40 to fulloperating power. With continued reference to FIG. 15B, the hot S11characterization signal of DUT 40 is reflected from the input of DUT 40along path CX and, passing through Test Port 1 44, enters PSI 20 at portJ15. The hot S11 signal passes through the C-2 path of switch 230,traveling along path CXI, and exits PSI 20 at port J14. The hot S11signal enters VNA 30, as shown in FIG. 15A, at VNA Port 1 340 andtravels along path CXII through the VNA internal directional coupler,exiting at the coupled port and passing thru jumper 380 b. In oneembodiment, the hot S11 signal is attenuated by step attenuator 322. Thehot S11 signal then enters A Receiver 330 along path CXIII and ismeasured by A Receiver 330.

A phase-locked reference signal R1 is derived from the amplified drivesignal passing through directional coupler 110 (FIG. 15B). The R1reference signal is coupled off from the amplified drive signal by thecoupled-line of directional coupler 110 along path CXIV. The R1 signalis attenuated by attenuator 160 before passing through switch 220, withswitch 220 in the 3-2 position along path CXV. The R1 signal exits PSI20 at port J9 and enters VNA 30 at R1 In 360 (FIG. 15A). The R1 signaltravels along path CXVI and is measured by R1 Receiver 332. The finalhot S11 measurement value is the ratio of the A Receiver 330 signaldivided by the R1 Receiver 332 (reference) signal.

FIGS. 16A and 16B are schematics illustrating signal propagation throughVNA 30 and PSI 20 for hot S21 measurements. As shown in FIG. 16A VNAsource 300 generates a drive signal, which enters switch splitterleveler 310 along path DI. The signal exits switch splitter leveler 310along path DII. In one embodiment the signal is attenuated by stepattenuator 320. The signal travels along path DIII and exits VNA 30 at ASource Out 350.

The signal enters PSI 20 at port J7, as shown in FIG. 16B, and travelsalong path DIV passing through switch 200, with switch 200 in the 2-3position. The signal enters the input of internal amplifier 100 and theamplified signal exits 100 along path DV. The amplified signal passesthrough the main-line input of directional coupler 110 along path DVIpassing through switch 210, with switch 210 in the 3-2 position. Theamplified signal continues to travel along path DVI and exits PSI 20 atport J12.

As shown in FIG. 16A, the amplified signal enters VNA 30 at A Coupler In352 and travels along path DVII, exiting VNA 30 at Port 1 340. Theamplified signal re-enters PSI 20, as shown in FIG. 16B, at port J14 andtravels along path DVIII through switch 230, with switch 230 in the 2-Cposition. The amplified signal exits PSI 20 at port J15 and, passingthrough Test Port 1 44 along path DIX, enters the input of DUT 40. Theamplified signal entering the input of DUT 40 drives DUT 40 to fulloperating power.

The hot S21 parameter is generated from the output of DUT 40 along pathDX and, passing through Test Port 2 48, enters PSI 20 at port J16. Thehot S21 signal travels along path DXI and enters the main-line input ofair-line directional coupler 140. The hot S21 signal is coupled off andexits the coupled-line output of air-line directional coupler 140 alongpath DXII. The coupled hot S21 signal passes through the input ofdirectional coupler 150 along path DXIII. Attenuator 180 attenuates thehot S21 signal and the attenuated hot S21 signal travels through switch240, with switch 240 in the I-C position, along path DXIV, exiting PSI20 at port J18.

The attenuated hot S21 signal enters VNA 30, as shown in FIG. 16A, at BIn 368 and travels along path DXV. In one embodiment, the attenuated hotS21 signal is further attenuated by step attenuator 324. The attenuatedhot S21 signal travels along path DXVI and is measured by B receiver336.

A phase-locked reference signal R1 is derived from the amplified drivesignal passing through directional coupler 110 (FIG. 16B). The R1reference signal is coupled off from the amplified drive signal by thecoupled-line of directional coupler 110 along path DXVII. The R1 signalis attenuated by attenuator 160 before passing through switch 220 in the3-2 position along path DXVIII. The R1 signal exits PSI 20 at port J9and enters VNA 30 at R1 In 360 (FIG. 16A). The R1 signal travels alongpath DXIX and is measured by R1 Receiver 332. The final hot S21measurement value is the ratio of the B Receiver 336 signal divided bythe R1 Receiver 332 (reference) signal.

FIGS. 17A and 17B are schematics illustrating signal propagation throughPSI 20 and VNA 30 for hot S22 measurement. Signal generator 60 generatesa drive signal at frequency F1 that enters PSI 20 at port J1, andtraveling path E1, exits PSI 20 at port J2. External linear driveramplifier 50 amplifies the drive signal. The amplified drive signalenters PSI 20 at port J3 and passes through the main-line input ofdirectional coupler 120 along path EII. The amplified drive signal exitsthe main-line output of directional coupler 120 along path EIII andpasses through switch 230, with switch 230 in the 1-C position. Theamplified drive signal exits PSI 20 along path EIV at port J15 andpassing through Test Port 1 44 enters the input of DUT 40 along path EV.The amplified drive signal drives DUT 40 to full operating power.

VNA Source 300, as shown in FIG. 17B, generates an output injectionsignal at frequency F2 which enters switch splitter leveler 310 alongpath EVI. Frequency F1 of the drive signal is slightly different fromfrequency F2 of the output injection signal. Because the drive signaldrives the DUT 40 to full operating power at frequency Fl, if the samefrequency were injected into the output of DUT 40, the reflected signalwould be swamped. For example, if the DUT 40 is outputting 100 watts andthe output injection signal is one watt, then the output injectionsignal would be overwhelmed by the 100 watt output of the DUT 40.Therefore, if the drive signal Fl is, for example, 2000 MHz, the outputinjection signal is 2005 MHz.

With reference to FIG. 17B, the output injection signal exits switchsplitter leveler 310 along path EVII. In one embodiment the outputinjection signal is attenuated by step attenuator 326. The outputinjection signal travels along path EVIII and exits VNA 30 at VNA Port 2344. The output injection signal enters PSI 20, as shown in FIG. 17A, atport J6. The output injection signal travels along path EIX throughswitch 200, with switch 200 in the 4-3 position. The output injectionsignal is amplified by the internal amplifier 100. The amplified outputinjection signal travels along path EX and passes through the main-lineof directional coupler 110. The amplified output injection signal exitsdirectional coupler 110 at the main-line output and passes throughswitch 210, with switch 210 in the 3-4 position. The amplified outputinjection signal travels along path EXI to the wide-band isolator 190.The wide-band isolator U1 allows in-band signals (for example, from 0.8to 2.2 GHz) to pass, and prevents signals flowing in the other direction(from the output of DUT 40) from passing.

The amplified output injection signal enters air-line directionalcoupler 130 at the coupled-line port along path EXII and exits themain-line input of air-line directional coupler 130. (As discussedpreviously, when a signal is input at the coupled-line of a directionalcoupler an attenuated version of the signal appears at the main-lineinput of the directional coupler. However, no signal will appear at theoutput of the directional coupler.) The amplified signal travels alongpath EXIII and passes through the main-line of air-line directionalcoupler 140. The amplified signal exits the main-line of air-linedirectional coupler 140 unattenuated and exits PSI 20 at port J1 6 alongpath EXIV. The amplified output injection signal passes through TestPort 2 48 along path EXV and is injected into the output of DUT 40.

The hot S22 parameter reflects from the output of DUT 40 along path EXVIand, passing through Test Port 2 48, enters PSI 20 at port J16. The hotS22 signal travels along path EXVII and enters the main-line input of140. The hot S22 signal is coupled off and exits air-line directionalcoupler 140 at the coupled-line output along path EXVIII. The coupledhot S22 signal passes through the main-line of directional coupler 150along path EXIX. Attenuator 180 attenuates the hot S22 signal and theattenuated hot S22 signal travels through switch 240, with 240 in the1-C position, along path EXX, exiting PSI 20 at port J18. The attenuatedhot S22 signal enters VNA 30, as shown in FIG. 17B, at B In 368 andtravels along path EXXI. In one embodiment, the attenuated hot S22signal is further attenuated by step attenuator 324. The hot S22 signaltravels along path EXXII and is measured by B receiver 336.

A phase-locked reference signal R2 is derived from the amplified drivesignal passing through directional coupler 110 (FIG. 17A). The R2reference signal is coupled off from the amplified drive signal by thecoupled-line of directional coupler 110 along path EXXIII. The R2 signalis attenuated by attenuator 160 before passing through switch 220, withswitch 220 in the 3-4 position, and then through switch 250, with switch250 in the 2-C position, along path EXXIV. The R2 signal exits PSI 20 atport J10 and enters VNA 30 at R2 In 364 (FIG. 17B). The R2 signaltravels along path EXXV and is measured by R2 Receiver 334. The finalhot S22 measurement value is the ratio of the B Receiver 336 signaldivided by the R2 Receiver 334 (reference) signal.

FIGS. 18A and 18B are schematics illustrating signal propagation throughVNA 30 and PSI 20 for small-signal s11 measurements. As shown in FIG.18A, VNA source 300 generates a signal which enters switch splitterleveler 310 along path Fl. The signal exits switch splitter leveler 310along path FII. In one embodiment, the signal is attenuated by stepattenuator 320. The signal travels along path FIII and exits VNA 30 at ASource Out 350.

The signal enters PSI 20 at port J7, as shown in FIG. 18B, and travelsalong path FIV passing through switch 200, with switch 200 in the 2-1position. The signal bypasses internal amplifier 100 since an amplifieddrive signal is not required to drive DUT 40 to full operating power forsmall-signal characterization measurements. The signal passes throughswitch 210, with switch 210 in the 1-2 position, and continues to travelalong path FIV, exiting PSI 20 at port J12. As shown in FIG. 18A, thesignal enters VNA 30 at A Coupler In 352 and travels along path FV,exiting VNA 30 at Port 1 340. The signal enters PSI 20, as shown in FIG.18B, at port J14 and travels along path FVI through switch 230, withswitch 230 in the 2-C position. The signal exits PSI 20 at port J15 and,passing through Test Port 1 44 along path FVII, enters the input of DUT40.

The small-signal s11 characterization signal of DUT 40 is reflected fromthe input of DUT 40 along path FVIII and, passing through Test Port 144, enters PSI 20 at port J15. The s11 signal passes through switch 230along the C-2 path, traveling along path FIX, and exits PSI 20 at portJ14. The s11 signal enters VNA 30, as shown in FIG. 18A, at VNA Port 1340 and travels along path FX. In one embodiment, the s11 signal isattenuated by step attenuator 322. The s11 signal then travels throughthe VNA internal directional coupler, exiting at the coupled port, thenthrough jumper 380 b. The s11 signal then enters A Receiver 330 alongpath FXI and is measured by A Receiver 330.

A phase-locked reference signal R1 is derived from the signal passingfrom the switch splitter leveler 310 along path FXII, exiting the VNA 30at R1 Out 358 (FIG. 18A), and entering the PSI 20 at J8 (FIG. 18B). TheR1 reference signal passes through switch 220 in the 1-2 position alongpath FXII. The R1 signal exits PSI 20 at port J9 and enters VNA 30 at R1In 360 (FIG. 18A). The R1 signal travels along path FXII and is measuredby R1 Receiver 332. The small signal S11 measurement value is the ratioof the A Receiver 336 signal divided by the R1 Receiver 332 (reference)signal.

FIGS. 19A and 19B are schematics illustrating signal propagation throughVNA 30 and PSI 20 for small-signal s21 measurements. As shown in FIG.19A VNA source 300 generates a signal, which enters switch splitterleveler 310 along path GI. The signal exits switch splitter leveler 310along path GII. In one embodiment, the signal is attenuated by stepattenuator 320. The signal travels along path GIII and exits VNA 30 at ASource Out 350.

The signal enters PSI 20 at port J7, as shown in FIG. 19B, and travelsalong path GIV passing through switch 200, with switch 200 in the 2-1position. The signal bypasses internal amplifier 100 since an amplifiedsignal is not required to drive DUT 40 to full operating power forsmall-signal characterization measurements. The signal passes throughswitch 210, with switch 210 in the 1-2 position, and continues to travelalong path GIV, exiting PSI 20 at port J12.

As shown in FIG. 19A, the signal enters VNA 30 at A Coupler In 352 andtravels along path GV, exiting VNA 30 at Port 1 340. The signal entersPSI 20, as shown in FIG. 19B, at port J14 and travels along path GVIthrough switch 230, with switch 230 in the 2-C position. The signalexits PSI 20 at port J15 and, passing through Test Port 1 44 along pathGVII, enters the input of DUT 40.

With reference to FIG. 19B, the small-signal s21 parameter is generatedfrom the output of DUT 40 along path GVIII and, passing through TestPort 2 48, enters PSI 20 at port J16. The s21 signal travels along pathGIX and enters the main-line input of air-line directional coupler 140.The s21 signal is coupled off and exits at the coupled-line output ofair-line directional coupler 140 along path GX. The coupled s21 signalpasses through the input of directional coupler 150 along path GXI.Attenuator 180 attenuates the s21 signal and the attenuated s21 signaltravels through switch 240, with switch 240 in the 1-C position, alongpath GXII, exiting PSI 20 at port J18. The attenuated s21 signal entersVNA 30, as shown in FIG. 19A, at B In 368 and travels along path GXIII.In one embodiment, the attenuated s21 signal is further attenuated bystep attenuator 324. The attenuated s21 signal travels along path GXIVand is measured by B receiver 336.

A phase-locked reference signal R1 is derived from the signal passingfrom the switch splitter leveler 310 along path GXV, exiting the VNA 30at R1 Out 358 (FIG. 19A), and entering the PSI 20 at J8 (FIG. 19B). TheR1 reference signal passes through switch 220 in the 1-2 position alongpath GXVI. The R1 signal exits PSI 20 at port J9 and enters VNA 30 at R1In 360 (FIG. 19A). The R1 signal travels along path GXVII and ismeasured by R1 Receiver 332. The small signal S21 measurement value isthe ratio of the B Receiver 336 signal divided by the R1 Receiver 332(reference) signal.

FIGS. 20A and 20B are schematics illustrating signal propagation throughPSI 20 and VNA 30 for small-signal s22 measurement. VNA Source 300, asshown in FIG. 20A, generates an output injection signal which entersswitch splitter leveler 310 along path HI. The output injection signalexits switch splitter leveler 310 along path HII. In one embodiment, thesignal is attenuated by step attenuator 326. The output injection signaltravels along path HIII and exits VNA 30 at VNA Port 2 344. The outputinjection signal enters PSI 20, as shown in FIG. 20B, at port J6. Theoutput injection signal travels along path HIV through switch 200, withswitch 200 in the 4-3 position. The output injection signal is amplifiedby 100 as for hot S22 measurements to provide a high level signal to theDUT 40 output. Even though an amplified output injection signal is notrequired for some small-signal s22 measurements, the reflected signalfrom an extremely good small-signal device can be too low to measureaccurately, so the amplifier is usually needed.

With reference to FIG. 20B, the amplified output injection signaltravels along path HV and passes through the main-line of directionalcoupler 110. The amplified output injection signal exits at themain-line output of directional coupler 110 and passes through switch210, with switch 210 in the 3-4 position. The amplified output injectionsignal travels along path HVI to the wide-band isolator 190. Thewide-band isolator 190 allows in-band signals (for example, from 0.8 to2.2 GHz) to pass. The amplified output injection signal enters air-linedirectional coupler 130 at the coupled-line port along path HVII andexits the main-line input of air-line directional coupler 130. (When asignal is input at the coupled-line of a directional coupler anattenuated version of the signal appears at the main-line input.However, no signal will appear at the output of the directionalcoupler.) The amplified signal travels along path HVIII and passesthrough the main-line of air-line directional coupler 140. The amplifiedsignal exits the main-line of air-line directional coupler 140unattenuated and exits PSI 20 at port J16 along path HIX. The amplifiedoutput injection signal passes through Test Port 2 48 along path HX andis injected into the output of DUT 40.

The small-signal s22 parameter is reflected from the output of DUT 40along path HXI and, passing through Test Port 2 48, enters PSI 20 atport J16. The s22 signal travels along path HXII and enters themain-line input of air-line directional coupler 140. The s22 signal iscoupled off and exits at the coupled-line output of air-line directionalcoupler 140 along path HXIII. The coupled s22 signal passes through themain-line of directional coupler 150 along path HXIV. Attenuator 180attenuates the s22 signal and the attenuated s22 signal travels throughswitch 240, with switch 240 in the 1-C position, along path HXV, exitingPSI 20 at port J18. The attenuated s22 signal enters VNA 30, as shown inFIG. 20A, at B In 368 and travels along path HXVI. In one embodiment,the attenuated s22 signal is further attenuated by step attenuator 324.The attenuated s22 signal travels along path HXVII and is measured by Breceiver 336.

A phase-locked reference signal R2 is derived from the amplified drivesignal passing through directional coupler 110 (FIG. 20B). The R2reference signal is coupled off from the amplified drive signal by thecoupled-line of directional coupler 110 along path HXVIII. The R2 signalis attenuated by attenuator 160 before passing through switch 220, withswitch 220 in the 3-4 position, and then through switch 250, with switch250 in the 2-C position. The R2 signal exits PSI 20 at port J10 andenters VNA 30 at R2 In 364 (FIG. 20B). The R2 signal travels along pathHXIX and is measured by R2 Receiver 334. The small signal S22measurement value is the ratio of the B Receiver 336 signal divided bythe R2 Receiver 334 (reference) signal.

The foregoing description of the present invention provides illustrationand description, but is not intended to be exhaustive or to limit theinvention to the precise one disclosed. Modifications and variations arepossible consistent with the above teachings or may be acquired frompractice of the invention. Thus, it is noted that the scope of theinvention is defined by the claims and their equivalents.

1-19. (canceled)
 20. A method comprising a first mode that includessteps of: providing a first signal at a predetermined first frequency(F1) to an input of a device under test, wherein the first signal isprovided by a measurement interface apparatus; receiving a harmonicssignal at the measurement interface apparatus from an output of thedevice under test; passing the harmonics signal through an input port ofa main-line of a first air-line directional coupler disposed within themeasurement interface apparatus; and providing the harmonics signal froman output port of the main-line of the first air-line directionalcoupler to a spectrum analyzer coupled to the measurement interfaceapparatus.
 21. The method of claim 20, further comprising the steps of:providing an initial signal at the predetermined first frequency to aninput of a first amplifier, wherein the initial signal is generated by asignal generator coupled to the measurement interface apparatus;receiving an amplified version of the initial signal from an output ofthe amplifier, wherein the first signal provided to the input of thedevice under test is the amplified version of the initial signal. 22.The method of claim 20, further comprising a second mode that includessteps of: providing a second signal at a predetermined second frequency(F2) to an input of a second amplifier disposed within the measurementinterface apparatus to provide an amplified second signal, wherein thesecond signal is generated by a network analyzer coupled to themeasurement interface apparatus; passing the amplified second signalthrough an input port of a directional coupler disposed within themeasurement interface apparatus; and providing the amplified secondsignal from an output port of the directional coupler to the input ofthe device under test, wherein the amplified second signal drives thedevice under test to full power output.
 23. The method of claim 22,further comprising the steps of: receiving a reflected signal (S11) atthe measurement interface apparatus from the input of the device undertest; and providing the reflected signal to a receiver disposed withinthe network analyzer.
 24. The method of claim 22, further comprising athird mode that includes steps of: receiving a generated signal (S21) atthe measurement interface from the output of the device under test;passing the generated signal through an input port of a main-line of asecond air-line directional coupler disposed within the measurementinterface apparatus to produce a coupled generated signal; and providingthe coupled generated signal to a receiver disposed within the networkanalyzer.
 25. The method of claim 24, further comprising the step of:providing the coupled generated signal from an output port of acoupled-line of the second air-line directional coupler to an attenuatorto produce an attenuated generated signal, wherein the coupled generatedsignal provided to the receiver disposed within the network analyzer isattenuated.
 26. The method of claim 22, further comprising the steps of:providing the amplified second signal from a coupled output port of thedirectional coupler to produce a reference signal (R1); and providingthe reference signal (R1) to a receiver disposed within the networkanalyzer.
 27. The method of claim 21, wherein the first signal drivesthe device under test to full power output, further comprising a fourthmode that includes steps of: providing a second signal at apredetermined second frequency (F2) to an input of a second amplifierdisposed within the measurement interface apparatus to provide anamplified second signal, wherein the second signal is generated by anetwork analyzer coupled to the measurement interface apparatus; passingthe amplified second signal through an input port of a directionalcoupler disposed within the measurement interface apparatus; providingthe amplified second signal from an output port of the directionalcoupler to a wide band isolator disposed within the measurementinterface apparatus to provide an isolated second signal; passing theisolated second signal through a coupled-line of the first airlinedirectional coupler to the main-line of the first air-line directionalcoupler to provide a coupled second signal; providing the coupled secondsignal to the output of the device under test, wherein the device undertest reflects a portion of the coupled second signal as a reflectedsignal (S22); passing the reflected signal through an input port of amain-line of a second air-line directional coupler to a coupled-line ofthe second air-line directional coupler disposed within the measurementinterface apparatus to provide a coupled reflected signal; and providingthe coupled reflected signal to a first receiver disposed within anetwork analyzer coupled to the measurement interface apparatus.
 28. Themethod of claim 27, further comprising the steps of: providing theamplified second signal from a coupled output port of the directionalcoupler to produce a reference signal (R2); and providing the referencesignal to a second receiver disposed within the network analyzer. 29.The method of claim 20, further comprising a fifth mode that includessteps of: blocking the first signal such that it does not enter theinput of the device under test; providing a second signal (FS 1) to theinput of the device under test, wherein the second signal is generatedby a network analyzer coupled to the measurement interface apparatus andthe second signal is provided by the measurement interface apparatus.receiving a reflected signal (s11) at the measurement interface devicefrom the input of the device under test; and providing the reflectedsignal to a receiver disposed within the network analyzer.
 30. Themethod of claim 20, further comprising a sixth mode that includes stepsof: blocking the first signal such that it does not enter the input ofthe device under test; providing a second signal (FS 1) to the input ofthe device under test, wherein the second signal is generated by anetwork analyzer coupled to the measurement interface apparatus and thesecond signal is provided by the measurement interface apparatus;receiving a generated signal (s21) at the measurement interfaceapparatus from the output of the device under test; and providing thegenerated signal to a receiver disposed within the network analyzer. 31.The method of claim 20, further comprising a seventh mode that includessteps of: blocking the first signal such that it does not enter theinput of the device under test; providing a second signal at apredetermined second frequency (F2) to an input of a amplifier disposedwithin the measurement interface apparatus to provide an amplifiedsecond signal, wherein the second signal is generated by a networkanalyzer coupled to the measurement interface apparatus; providing theamplified second signal from an output port of a directional coupler toa wide band isolator disposed within the measurement interface apparatusto provide an isolated second signal; passing the isolated second signalthrough a coupled-line of the first airline directional coupler to themain-line of the first air-line directional coupler disposed within themeasurement interface apparatus to provide a coupled second signal;providing the coupled second signal to the output of the device undertest, wherein the device under test reflects a portion of the coupledsignal as a reflected signal (s22); passing the reflected signal throughan input port of a main-line of a second air-line directional couplerdisposed within the measurement interface apparatus to a coupled-line ofthe second air-line directional coupler to provide a coupled reflectedsignal; providing the coupled reflected signal to a receiver disposedwithin the network analyzer.
 32. The method of claim 31, furthercomprising the steps of: providing the amplified second signal from acoupled output port of the directional coupler to produce a referencesignal (R2); and providing the reference signal to a second receiverdisposed within the network analyzer. 33-44. (canceled)